(a) Technical Field
The embodiments of the present invention relate generally to an antenna in a mobile communication system and more particularly, to a Multi-Line Phase Shifter (MLPS) being a core part for controlling the vertical beam tilt of an antenna.
(b) Description of the Related Art
Although a fixed antenna was initially used for a Base Station (BS) in a mobile communication system, a vertical beam tilt-controlled antenna capable of vertical and/or horizontal beam tilting has recently been popular due to its benefits. For the vertical beam tilt-controlled antenna, mechanical beam tilting and electrical beam tilting are available.
Mechanical beam tilting relies on a manual or force-driven bracket structure at a portion engaged with a support pole in an antenna. The installation inclination of the antenna is changed according to an operation of the bracket structure, thereby enabling the vertical beam tilting of the antenna. Meanwhile, electrical beam tilting is based on an MLPS. Vertical beam tilting is electrically achieved for an antenna by changing the phase difference between signals provided to vertically arranged antenna radiation elements. An example of the vertical beam tilting technology is disclosed in U.S. Pat. No. 6,864,837 entitled “Vertical Electrical Downtilt Antenna”, filed by EMS Technologies, Inc. (invented by Donald L. Runyon, et al. and issued on Mar. 8, 2005).
An MLPS is a requisite for electrical vertical beam tilting. The MLPS is used in a variety of fields of a Radio Frequency (RF) analog signal processing end, for phase modulation as well as beam control of a phase array antenna. The MLPS operates based on the principle that a phase difference is incurred between an input signal and an output signal by appropriately delaying the input signal. The phase difference can be obtained by simply differentiating the physical length of a transmission line or differentiating a signal propagation speed along a transmission line in various manners. The MLPS is usually configured so as to change a phase shift by changing the length of a transmission line, for example.
Especially, mobile communication systems have recently required a technique for harmoniously changing the phase of each radiation element in a phase array antenna in order to adjust the coverage of a BS through control of the vertical beam angle of the phase array antenna in the BS. To meet this demand, MLPSs of various structures have been developed and widely used. Particularly, an MLPS may have a structure for dividing an input signal into a plurality of output signals and appropriately controlling the phase difference of each output signal. For example, a technology related to an MLPS for vertical beam tilting is disclosed in U.S. Pat. No. 6,831,692 entitled “Low Cost Trombone Line Beamformer” filed by Etenna Corporation (invented by William E. McKinzie, III, et al. and issued on Dec. 14, 2004).
However, the developmental efforts of the MLPS were expended mainly toward improvement of its structure or improvement of the performance of changing the phase of a processed signal, but with no regard to the structure of an antenna in which the MLPS is installed, such as a phase array antenna. Accordingly, there exists a need for studying and developing an MLPS with an improved performance and structure.